Traditional electrophotographic (EP) devices have a spinning polygon mirror that directs a laser beam to a photoconductor, such as a drum, to create one or more scan lines of a latent to-be-printed image. Recently, however, it has been suggested that torsion oscillator or resonant galvanometer structures can replace the traditional spinning polygon mirror and create scan lines in both the forward and reverse directions (e.g., bi-directionally), thereby increasing efficiency of the EP device. Because of their MEMS scale size and fabrication techniques, the structures are also fairly suggested to reduce the relative cost of manufacturing. Unfortunately, scanning in two directions adds a measure of complexity to image referencing since reference points need occur for each of the forward and reverse scans at opposite ends of the printed page and the slightest of deviations amplifies print image imperfections. Also, any asymmetry in the motion of the oscillator or galvanometer results in errors in print linearity and line-to-line registration across the printing area.
Under ideal conditions, the oscillator or galvanometer is well controlled by a drive configuration to move it sinusoidally without impedance. Because of modern design constraints, however, sinusoidal drives are somewhat impractical or economically infeasible. In turn, more practical drive configurations consist of a sequence of pulses, each of which causes a corresponding force to be imparted to the galvanometer or oscillator to make it move. Problematically, there is a notable drawback in the discontinuous nature by which forces are applied to the galvanometer or oscillator and asymmetric distortion of laser scanning motion can be introduced if left uncontrolled.
Since the mechanical properties of the constituent materials that compose the galvanometer or oscillator are influenced by temperature, and the damping of the motion is dependent on air density (in turn, a result of both temperature and pressure, where pressure varies with altitude, for instance), it is clear that ambient operating conditions affect the shape and magnitude of the linearity and misalignment of scan lines. In this regard, print quality changes occur as a result of changes in operating altitude, temperature or from large barometric changes, for example. While electronic measurement of temperature can be implemented with relatively simple and low cost components, measurement of pressure generally cannot, and introducing relatively high cost components to compensate for nonlinearity and misalignment would negate any prospective cost savings from using the galvanometer or oscillator.
Accordingly, there exists a need in the art for characterizing the manner in which bi-directionally scanning EP devices should operate according to various operating conditions, especially pressure. Particularly, there are needs by which knowing the actual operating conditions of the EP device will relate to making corrections to improve print quality. Ultimately, the need extends to simply and efficaciously obtaining pressure without introducing high-cost components. Naturally, any improvements should further contemplate good engineering practices, such as relative inexpensiveness, stability, low complexity, ease of implementation, etc.